Composite conductor and contact between conductors



June 10, 1941.

H. FIGOUR COMPOSITE CONDUCTOR AND CONTACT BETWEEN CONDUCTORS Fi led Aug.'2, 19:59

Fig. 4.

/n ventor H'gaur fltt'ornez/ Patented June 10, 1941 COMPOSITE CONDUCTORAND CONTACT BETWEEN CONDUCTORS Henri Figour, Paris, France, assignor toInternational Standard Electric Corporation, New

York, N. Y.

Application August 2, 1939, Serial No. 287,888 In France August It, 19386 Claims.

The present invention relates to composite conductors and moreparticularly to means for ensuring contact between successive elementscomprising these conductors, or between two conductor elements withtemporary contact.

In particular, the object oi the invention is to provide compositeconductors in which a satisfactory electrical contact is ensured in asimple manner and having no appreciable danger of deterioration of thecomponent conducting materials. w

In order to ensure contact between the conductor and/or semi-conductorelements, for example, between a conductor conveying the current and thesurface of the substance forming an arrester layer in a dry rectifier,precautions must be taken not to have an excessive contact resistance.Such contact is normally ensured by pressure on the arrester layer, orby volatilisation in vacuo of any metal which is deposited on thearrester layer, or by pulverisa'tion of a metal or an alloy. Thesemethods, however, have considerable drawbacks. For example, in the casein which the contact is ensured by pressure, the pressure necessary inorder to obtain a satisfactory contact usually involves dangerousmechanical tensions. In the case in which the contact is ensured bymetallic deposit on a semi-conducting layer of an additional metalliclayer by 'volatilisation in vacuo this layer must be as thin as Possibleso as to prevent mechanical tensions which might involve separation atthe time of the pressing on this layer of the second conductor. If thislayer is very thin and forms a resistive film, its ohmic resistance inthe direction parallel to the surface of the first element is relativelyhigh and it is necessary that the contact ensuring the junction to theexternal circuit may be made on the largest possible surface, whichinvolves relatively high pressures which are also capable of ageing ordeteriorating the resultant composite conductor.

The main object of the invention is to Provide means "for avoiding.these excessive pressures.

In accordance with certain characteristics of the invention, a compositeconductor comprising at least two layers of conducting orsemi-conducting elements, is characterised in this, that one of-the twoelements is of a spongy structure or has a rough surface, the particlesof which are microscopic and irregularly arranged, the surface portioncomposed of these particles having the crushing characteristics of aspongy structure when pressed against a hard surface.

Two layers, one of which has the above-mentioned characteristics, maythen be assembled so as to ensure a satisfactory contact by means ofreduced pressure which crushes the spongy struc.- tures but does notrisk causing deterioration or premature ageing of the resultant product.

The invention in particular provides, in accordance with certaincharacteristics. devices conducting the electrical current uni-directiomally in which a metallic conducting layer, covered with asemi-conducting layer forming a current arrester layer, is pressedagainst a conducting layer made spongy either superficially or deeply,as mentioned above.

In accordance with other characteristics, the invention provides amethod of manufacturing uni-directional current-conducting elements,comprising the normal operations for forming on a base conducting membera semi-conducting layer serving as arrester layer, the preparation of aconducting plate or element for rendering the latter of spongy structureon the surface or in the mass, and the application of this spongyelement against the semi-conducting layer by means of a low pressure. Inorder to render the conducting element spongy, this element may bechemically or electro-chemically treated, and this chemical orelectro-chemical attack may or may not be preceded by a suitablemechanical or thermic treatment.

The invention will be described in more detail in relation to theattached drawing in which:

Figure 1 shows in cross-section a uni-directional device such as a dryrectifier, and

Figures 2, 3 and 4 show in section spongy structures which may beemployed in the device of Figure 1.

Figure 1 to which I will now refer represents, by way of embodiment of adevice employing characteristics of the invention, a d y rectifierelement comprising a metallic layer I, for example, of copper; coveredwith a semiconducting arrester layer 2, for; example, a layer of copperoxide, covered in turn with a film of vapourised metal 3, and aconducting layer 6. The layer 4 consists, in accordance with certaincharacteristics of the invention, of a metal sheet or member having sucha structure as those shown in Figures 2, 3 or 4. By the use of thissheet, good contact may be obtained between the film of vapourised metaland the sheet 4 with a very low pressure, Without involving the ohmicresistance in the direction parallel to the layer of oxide.

The various spongy structures considered in the invention are indicatedschematically in cross-section in Figures 2, 3 and 4. Figure 2 shows astructure which has already been made superficially spongy; thetreatment of the sheet has been such that a chemical or electrochemicalor other attack has caused the appearance on this sheet of an irregularsuperficial layer of microscopic structure, the particles of which aredistributed at random and which offers such crushing facility that aslight pressure against any conducting surface flattens the unevenportions, so as to form a conducting layer modelled on this conductingsurface with which it makes contact at all points.

In Figure 3, this superficial layer has been obtained for a substance ofnatural crystalline structure, but the crystals of the substance have noparticular desired orientation.

In Figure 4, the attack has been accomplished in the whole mass of thesubstance and thus it is an actual spongy structure. The crushingproperties of the two latter layers are the same as those of the layerof Figure 2.

The means for manufacturing such structures may consist of a chemical orelectro-chemical treatment which may or may not be preceded by amechanical or thermic treatment of the substance.

Nearly all the usual metals such as aluminium, silver, nickel, lead andothers are capable of giving such structures.

The baths employed, whether acid or alkaline, may be of variouscompositions according to the nature of the metal, its degree of purity,and in accordance with the nature of the desired spongy structure.

By way of example, a spongy surface may be obtained by chemicallyattacking a sheet of aluminium in the following bath:

Water cubic centimeters 555 Sulphuric acid do 65 Nitric acid do 65Ammonium chloride do 35 The sheet of aluminium will be plunged in thebath at the temperature of 70 C. for about five minutes in order toobtain a suitable spongy structure.

By increasing the proportions of nitric acid and decreasing that ofammonium chloride the structure becomes coarser and the attack is deepfor the greater part.

A spongy structure can be obtained on a sheet of silver by attacking itelectro-chemically, in a bath of the following composition:

Water grams 960 Nitric acid cubic centimeters 30 Sulphuric acid -do Thesheet of silver constituting the anode of the cell, the cathode beingconstituted of any metal, or a plate of gas carbon.

This treatment may be preceded by annealing at 600 for one hour, so asto start with-a metal which is always in the same physical condition.This heat treatment may be followed by a carding of the surface by meansof metallic cards so as to create a differential cold hammering of thesurface which, with preferential points of attack favours the depth ofetching,

It is clear that the two treatments have only been given by way ofexample, and that various the invention is not limited to these and thatany composite conductor comprising layers of conducting orsemi-conducting substances of which the contact must be ensured in asatisfactory manner may employ,-for one at least of the layers, a layerof which the treatment or superficial structure has been rendered spongyor rough in the manner described so as to ensure the desired contact.

It is also clear that the invention is not limited to the permanentexamples of conducting'and/or semi-conducting layers, one of which hasbeen made spongy before assembly, but that such layers may be employedto ensure better temporary contacts such as contacts of electric relays,or the like.

The invention is also capable of numerous modifications and adaptationswhich will be clear to one skilled in the art without departing from thescope of the invention.

What is claimed is:

1. A conducting element comprising at least two conducting layers, oneof said layers having an easily crushed spongy coating thereon, saidcoating and the surface of said other layer being in contact with eachother, and means for pressing said two layers together at a pressuresufficient to crush the spongy surface.

2. A uni-directional current conducting element comprising a metallicbase member, a semiconductive coating thereon, a conducting mem herhaving a spongy irregular surface, said surface and coating being incontact with each other, and means for pressing said conducting memberagainst said coating at a pressure sufficient to crush the spongysurface.

3. The method of manufacturing a unidirectional current conductingelement which comprises applying a semi-conductive coating to a basemember, toughening the surface of a conductive member, said surfacebeing spongy after roughening, and pressing said surface against saidcoating at a pressure sufficient to crush the spongy surface.

4. The method according to claim 3 wherein said surface is roughened byetching.

5. The method of manufacturing a unidirectional current conductingelement which comprises applying a semi-conductive coating to a basemember, annealing a sheet of aluminum, carding a surface of said sheet,roughening the surface thereof by immersing said sheet in a solutioncomprising by volume 555 partswater, parts sulphuric acid, 65 partsnitric acid, and 35 parts ammonium chloride at 0., and pressing saidsurface against said coating.

6. The method of manufacturing a unidirectional current conductingelement which comprises applying -a semi-conductive coating

